On Fri, Nov 28, 2003 at 02:46:49PM +1100, Alec Thomas wrote: > Hello, > > I have a couple of questions about device-mapper. I've had a look at the > source and could not see an obvious answer. > > Firstly, is it possible to utilize one device-mapper module from another > without redirecting to the actual device? For example, if I create a new > device-mapper module that maps blocks over the network and I want to > layer dm-crypt on top, am I forced to first map my device, then map > dm-crypt to this device. It would be extremely convenient to be able to > "layer" them without this requirement, so I could effectively call > dm-crypt to do mapping directly from my module. i dont believe any such structure has been made yet, but i suppose that if you just call the right functions in the dm-crypt.c module and pass the right parameters you can make it work. > My second question is somewhat related. I am thinking about doing a > network based block device running on device mapper. What is the "best" > way of communicating with user-space from a device-mapper module? I > would like to do most of the network stuff in user-space to take > advantage of existing cluster communication infrastructure, so it would > need to be fairly high-speed for transfer of blocks to/from user-space. All blocks are transfered using a bio structure. > So, to summarize in a less rambling way :)... > > Can device-mapper modules "chain" together without bouncing back through > device nodes? you have to do it inside your module > What is the "best" way of communicating at high volume with user-space > from a device-mapper module? all data goes back and forth through struct bio. JonB